Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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A HYDROTREATING CATALYST SYSTEM SUITABLE FOR
USE IN HYDROTREATING HYDROCARBONACEOUS FEEDSTREAMS
FIELD OF THE INVENTION
[00011 This invention relates to a hydrotreating catalyst system suitable for
use
in hydrotreating hydrocarbonaceous feedstreams. More particularly, the present
invention is directed at a stacked bed catalyst system comprising at least one
first
catalyst selected from conventional hydrotreating catalyst having an average
pore
diameter of greater than 10 urn and at least one second catalyst comprising a
bulk
metal hydrotreating catalyst.
BACKGROUND OF THE INVENTION
[00021 Environmental and regulatory initiatives are requiring ever lower
levels
of both sulfur and aromatics in distillate fuels. For example, proposed sulfur
limits
for distillate fuels to be marketed in the European Union for the year 2005 is
50
wppm or less. There are also proposed limits that would require lower levels
of
total aromatics as well as lower levels of multi-ring aromatics found in
distillate
fuels and heavier hydrocarbon products. Further, the maximum allowable total
aromatics level for CARB reference diesel and Swedish Class I diesel are 10
and 5
vol.%, respectively. Further, the CARB reference fuels allows no more than 1.4
vol.% polyaromatics (PNAs). Consequently, much work is presently being done
in the hydrotreating art because of these proposed regulations.
[00031 Still further, with the advent of increased environmental concerns, the
,performance requirements for lubricating oil basestocks themselves have also
increased. For example, the American Petroleum Institute (API) requirements
for
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Group II basestocks include a saturates content of at least 90%, a sulfur
content of
0.03 wt.% or less and a viscosity index (VI) between 80 and 120. Currently,
there
is a trend in the lube oil market to use Group II basestocks instead of Group
I
basestocks in order to meet the demand for higher quality basestocks that
provide
for increased fuel economy, reduced emissions, etc. For example, American
Petroleum Institute (API) requirements for Group II basestocks include a
saturates
content of at least 90%, a sulfur content of 0.03 wt.% or less and a viscosity
index
(VI) between 80 and 120.
[0004] Thus, as the environmental and regulatory initiatives to increase, the
search for new and different processes, catalysts, and catalyst systems that
exhibit
improved sulfur and nitrogen removal and aromatics saturation activity is a
continuous, ongoing exercise. Therefore, there is a need to provide
hydrocarbonaceous products that meet the demand for increased fuel economy,
reduced emissions, etc.
BRIEF DESCRIPTION OF THE FIGURE
[0005] The Figure is a plot of the relative volume activity of various
catalysts
and catalyst systems versus the days the respective catalysts and catalyst
systems
were on stream.
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SUMMARY OF THE INVENTION
[0006] The present invention is directed at a stacked bed catalyst system
suitable
for use in the hydrotreating of hydrocarbonaceous feedstocks. The catalyst
system
comprises:
a) at least one first catalyst selected from conventional hydrotreating
catalysts having an average pore diameter of greater than 10 nm; and
b) at least one second catalyst selected from bulk metal hydrotreating
catalysts.
DETAILED DESCRIPTION OF THE INVENTION
[0007] It should be noted that the terms "feedstock" and "feedstream" as used
herein are synonymous.
[0008] The present invention is directed at a stacked bed catalyst system
suitable
for use in the hydrotreating of hydrocarbonaceous feedstocks. The catalyst
system
comprises at least one first catalyst selected from conventional hydrotreating
catalysts having an average pore diameter of greater than 10 nm and at least
one
second catalyst selected from bulk metal hydrotreating catalysts. The stacked
bed
hydrotreating catalyst system is suitable for use in the hydrotreating of
hydrocarbonaceous feedstocks.
[0009] As stated above, the present invention is a stacked bed catalyst system
comprising at least a first and second hydrotreating catalyst. By "stacked
bed" it is
meant that the first catalyst appears in a separate catalyst bed, reactor, or
reaction
zone, and the second hydrotreating catalyst appears in a separate catalyst
bed,
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reactor, or reaction zone downstream, in relation to the flow of the
lubricating oil
feedstock, from the first catalyst.
[0010] The first hydrotreating catalyst is a supported catalyst. Suitable
hydrotreating catalysts for use as the first catalyst of the present catalyst
system
include any conventional hydrotreating catalyst. Conventional hydrotreating
catalyst as used herein is meant to refer to those which are comprised of at
least one
Group VIII metal, preferably Fe, Co and Ni, more preferably Co and/or Ni, and
most preferably Ni; and at least one Group VI metal, preferably Mo and W, more
preferably Mo, on a high surface area support material, preferably alumina.
The
Group VIII metal is typically present in an amount ranging from 2 to 20 wt.%,
preferably from 4 to 12%. The Group VI metal will typically be present in an
amount ranging from 5 to 50 wt.%, preferably from 10 to 40 wt.%, and more
preferably from 20 to 30 wt.%. All metals weight percents are on support. By
"on
support" we mean that the percents are based on the weight of the support. For
example, if the support were to weigh 100 g. then 20 wt.% Group VIII metal
would
mean that 20 g. of Group VIII metal was on the support.
[0011] However, not all conventional hydrotreating catalysts fitting the above-
described criteria are suitable for use in the present invention. The
inventors hereof
have unexpectedly found that the average pore diameter of the first catalyst
must
have a specific size to be suitable for use herein. Thus, in the practice of
the
present invention, a conventional catalyst, as described above, but having an
average pore diameter greater than 10 nm, as measured by water adsorption
porosimetry, must be used as the first catalyst of the present stacked bed
catalyst
system. It is preferred that the average pore diameter of the first catalyst,
i.e. the
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conventional hydrotreating catalyst, of the present stacked bed catalyst
system be
greater than 11 nm, more preferably greater than 12 nm.
[0012] The second hydrotreating catalyst is a bulk metal catalyst. By bulk
metal,
it is meant that the catalysts are unsupported wherein the bulk catalyst
particles
comprise 30 - 100 wt.% of at least one Group VIII non-noble metal and at least
one
Group VIB metal, based on the total weight of the bulk catalyst particles,
calculated
as metal oxides and wherein the bulk catalyst particles have a surface area of
at
least 10 m2/g. It is furthermore preferred that the bulk metal hydrotreating
catalysts
used herein comprise 50 to 100 wt.%, and even more preferably 70 to 100 wt.%,
of
at least one Group VIII non-noble metal and at least one Group VIB metal,
based
on the total weight of the particles, calculated as metal oxides. The amount
of
Group VIB and Group VIII non-noble metals can easily be determined VIB
TEM-EDX.
[0013] Bulk catalyst compositions comprising one Group VIII non-noble metal
and two Group VIB metals are preferred. It has been found that in this case,
the
bulk catalyst particles are sintering-resistant. Thus the active surface area
of the
bulk catalyst particles is maintained during use. The molar ratio of Group VIB
to
Group VIII non-noble metals ranges generally from 10:1 - 1:10 and preferably
from
3:1 - 1:3. In the case of a core-shell structured particle, these ratios of
course apply
to the metals contained in the shell. If more than one Group VIB metal is
contained
in the bulk catalyst particles, the ratio of the different Group VIB metals is
generally not critical. The same holds when more than one Group VIII non-noble
metal is applied. In the case where molybdenum and tungsten are present as
Group
VIB metals, the molybenum:tungsten ratio preferably lies in the range of 9:1 -
1:9.
Preferably the Group VIII non-noble metal comprises nickel and/or cobalt. It
is
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further preferred that the Group VIB metal comprises a combination of
molybdenum and tungsten. Preferably, combinations of
nickel/molybdenum/tungsten and cobalt/molybdenum/tungsten and
nickel/cobalt/molybdenum/tungsten are used. These types of precipitates appear
to
be sinter-resistant. Thus, the active surface area of the precipitate is
remained
during use. The metals are preferably present as oxidic compounds of the
corresponding metals, or if the catalyst composition has been sulfided,
sulfidic
compounds of the corresponding metals.
[0014] It is also preferred that the bulk metal hydrotreating catalysts used
herein
have a surface area of at least 50 m2/g and more preferably of at least 100
m2/g. It
is also desired that the pore size distribution of the bulk metal
hydrotreating
catalysts be approximately the same as the one of conventional hydrotreating
catalysts. More in particular, these bulk metal hydrotreating catalysts have
preferably a pore volume of 0.05 - 5 ml/g, more preferably of 0.1 - 4 ml/g,
still
more preferably of 0.1 - 3 ml/g and most preferably 0.1 - 2 ml/g determined by
nitrogen adsorption. Preferably, pores smaller than 1 nm are not present.
Furthermore these bulk metal hydrotreating catalysts preferably have a median
diameter of at least 50 nm, more preferably at least 100 nm, and preferably
not
more than 5000 m and more preferably not more than 3000 n. Even more
preferably, the median particle diameter lies in the range of 0.1 - 50 m and
most
preferably in the range of 0 5 - 50 m.
[0015] The reaction stage containing the stacked bed hydrotreating catalyst
system used in the present invention can be comprised of one or more fixed bed
reactors or reaction zones each of which can comprise one or more catalyst
beds of
the same or different catalyst. Although other types of catalyst beds can be
used,
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fixed beds are preferred. Such other types of catalyst beds include fluidized
beds,
ebullating beds, slurry beds, and moving beds. Interstage cooling or heating
between reactors, reaction zones, or between catalyst beds in the same
reactor, can
be employed since some olefin saturation can take place, and olefin saturation
and
the desulfurization reaction are generally exothermic. A portion of the heat
generated during hydrotreating can be recovered. Where this heat recovery
option
is not available, conventional cooling may be performed through cooling
utilities
such as cooling water or air, or through use of a hydrogen quench stream. In
this
manner, optimum reaction temperatures can be more easily maintained.
[00161 The stacked bed catalyst system of the present invention comprises 5-95
vol.% of the first catalyst with the second catalyst comprising the remainder,
preferably 40-60 vol.%, more preferably 5 to 50 vol.%. Thus, if the catalyst
system
comprises 50 vol.% of the first catalyst, the second catalyst will comprise 50
vol.%
also.
[00171 As stated above, the present catalyst system is suitable for use in the
hydrotreating of hydrocarbonaceous feedstreams. By hydrocarbonaceous
feedstream, it is meant a primarily hydrocarbon material obtained or derived
from
crude petroleum oil, from tar sands, from coal liquefaction, shale oil and
hydrocarbon synthesis. Thus, hydrocarbonaceous feedstreams suitable for
treatment with the present invention include those feedstreams boiling from
the
naphtha boiling range to heavy feedstocks, such as gas oils and resids, and
also
those derived from Fischer-Tropsch processes. Typically, the boiling range
will be
from 40 C to 1000 C. Non-limiting examples of suitable feedstreams include
vacuum gas oils; distillates including naphtha, diesel, kerosene, and jet
fuel; heavy
gas oils, raffinates, lube oils, etc.
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[0018] Hydrocarbonaceous boiling range feedstreams suitable for treatment with
the present invention include, among other things, nitrogen and sulfur
contaminants. Typically, the nitrogen content of such streams is 50 to 1000
wppm
nitrogen, preferably 75 to 800 wppm nitrogen, and more preferably 100 to 700
wppm nitrogen. The nitrogen appears as both basic and non-basic nitrogen
species.
Non-limiting examples of basic nitrogen species may include quinolines and
substituted quinolines, and non-limiting examples of non-basic nitrogen
species
may include carbazoles and substituted carbazoles. The sulfur content of the
hydrocarbonaceous boiling range feedstream will generally range from 50 wppm
to
7000 wppm, more typically from 100 wppm to 5000 wppm, and most typically
from 100 to 3000 wppm. The sulfur will usually be present as organically bound
sulfur. That is, as sulfur compounds such as simple aliphatic, naphthenic, and
aromatic mercaptans, sulfides, di- and polysulfides and the like. Other
organically
bound sulfur compounds include the class of heterocyclic sulfur compounds such
as thiophene, tetrahydrothiophene, benzothiophene and their higher homologs
and
analogs. The hydrocarbonaceous feedstreams suitable for use herein also
contain
aromatics, which are typically present in an amount ranging from 0.05 wt.%, to
2.5
wt.%, based on the hydrocarbonaceous boiling range feedstream.
[0019] Preferred feedstocks suitable for treatment with the present invention
are
wax-containing feeds that boil in the lubricating oil range, typically having
a 10%
distillation point greater than 650 F (343 C) and an endpoint greater than 800
F
(426 C), measured by ASTM D 86 or ASTM 2887. These feedstocks can be
derived from mineral sources, synthetic sources, or a mixture of the two. Non-
limiting examples of suitable lubricating oil feedstocks include those derived
from
sources such as oils derived from solvent refining processes such as
raffinates,
partially solvent dewaxed oils, deasphalted oils, distillates, vacuum gas
oils, coker
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gas oils, slack waxes, foots oils and the like, dewaxed oils, automatic
transmission
fluid feedstocks, and Fischer-Tropsch waxes. Automatic transmission fluid
("ATF") feedstocks are lube oil feedstocks having an initial boiling point
between
200 C and 275 C, and a 10% distillation point greater than 300 C. ATF
feedstocks
are typically 75-1 ION feedstocks.
[0020] These feedstocks may also have high contents of nitrogen- and sulfur-
contaminants. Feeds containing up to 0.2 wt.% of nitrogen, based on feed and
up
to 3.0 wt.% of sulfur can be processed in the present process. Feeds having a
high
wax content typically have high viscosity indexes of up to 200 or more. Sulfur
and
nitrogen contents may be measured by standard ASTM methods D5453 and D4629,
respectively.
[0021] As stated above, the present invention is suitable in hydrotreating
processes. It should be noted that the term "hydrotreating" as used herein
refers to
processes wherein a hydrogen-containing treat gas is used in the presence of a
suitable catalyst that is primarily active for the removal of heteroatoms,
such as
sulfur, and nitrogen, and saturation of aromatics. If the present invention is
employed in a hydrotreating process, a hydrocarbonaceous feedstream is
contacted
with the stacked bed catalyst system in a reaction stage operated under
effective
hydrotreating conditions. By effective hydrotreating conditions, it is meant
those
conditions effective at removing at least a portion of the sulfur contaminants
from
the hydrocarbonaceous feedstream. Effective hydrotreating conditions generally
include temperatures of from 150 to 400 C, a hydrogen partial pressure of from
1480 to 20786 kPa (200 to 3000 psig), a space velocity of from 0.1 to 10
liquid
hourly space velocity (LHSV), and a hydrogen to feed ratio of from 89 to 1780
m3/m3 (500 to 10000 scf/B).
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[00221 The contacting of the hydrocarbonaceous feedstock with the stacked bed
hydrotreating catalyst system produces a hydrotreated effluent comprising at
least a
gaseous product and a hydrotreated hydrocarbonaceous feedstock. The
hydrotreated effluent is stripped to remove at least a portion of the gaseous
product
from the hydrotreated effluent. The means used to strip the hydrotreated
effluent
can be selected from any stripping method, process, or means known can be
used.
Non-limiting examples of suitable stripping methods, means, and processes
include
flash drums, fractionators, knock-out drums, steam stripping, etc.
[0023] The above description is directed to preferred embodiments of the
present invention. Those skilled in the art will recognize that other
embodiments
that are equally effective could be devised for carrying out the invention.
[0024] The following examples will illustrate the improved effectiveness of
the
present invention, but is not meant to limit the present invention in any
fashion.
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EXAMPLES
EXAMPLE 1
[00251 A medium vacuum gas oil having the properties outlined in Table 1 was
processed in an isothermal pilot plant over three catalysts systems at 1200
psig
hydrogen partial pressure. The catalyst systems and operating conditions are
given
in Table 2. Catalyst B is a conventional hydrotreating catalyst having 4.5
wt.%
Group VI metal, 23 wt.% Group VIII metal on an alumina support and has an
average pore size of 14.0 rim. The bulk metal hydrotreating catalyst was a
commercial bulk metal hydrotreating catalyst marketed under the name Nebula by
Akzo-Nobel.
[00261 In the Examples, all the catalyst systems were lined out at 50 days on
stream. A first order kinetic model with an activation energy of 31,000
cal/gmol
was used to compare volume activities between the catalysts.
TABLE 1
Medium Vacuum Gas Oil
Density at 70 C /ec 0.88
Nitrogen w m 700
Sulfur (wt.%) 2.6
GCD 5 WT% Boiling Point C 334
GCD 50 WT% Boiling Point C 441
GCD 95 WT% Boiling Point C 531
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TABLE 2
50 vol.% Catalyst B
100 vol.% 100 vol.% followed by
Catalyst System Catalyst B Nebula 1 50 vol.% Nebula 1
Average Catalyst 370 380 370
Temperature (IC )
Liquid Hourly Space 2 1 1
Velocity (hr -'
Stripped reactor 227 17 34
Effluent Nitrogen
Content (wppm)
Nitrogen Removal 1 1.18 1.34
Relative Volume
Activity
[0027] The Nitrogen Removal Relative Volume Activity ("RVA") for each
catalyst system was calculated by simple first order kinetic modeling. As
shown in
Table 2, the 50/50 vol.% stacked bed catalyst system, with the large average
pore
size Catalyst B upstream of the bulk metal catalyst, showed higher nitrogen
removal activity than either of the single catalyst systems demonstrated on
their
own.
EXAMPLE 2
[0028] The hydrotreating ability of different stacked beds of Catalyst B and
Nebula were analyzed by hydrotreating different feedstreams over the stacked
beds
in the in two parallel reactor trains of the same isothermal pilot plant unit
used in
Example 1 above. The feedstreams used were Medium Cycle Oils("MCO") from
an FCC unit and blends of the MCO with a virgin feedstock were tested in two
parallel reactor trains. The feed properties are described in Table 3, below.
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[0029] In this Example, one reactor train consisted entirely of a conventional
NiMo on Alumina hydrotreating catalyst, Catalyst C, with an average pore
diameter of 7.5 nm. The other reactor train contained a stacked bed system
with
75-vol. % of Catalyst C followed by 25-vol. % of Catalyst A, a bulk
multimetallic
sulfide catalyst having an average pore diameter of 5.5 nm.
[0030] The separate reactors in both trains were immersed in a fluidized
sandbath for efficient heat transfer. Thus, the temperature of the first 75-
vol. % of
Catalyst C was at the same temperature whether it was in train 1 or 2.
Likewise,
the last 25-vol. % of Catalyst C in train 1 was at the same temperature as the
last
25-vol. % of Catalyst A in train 2. Therefore, In Example 2, each of the two
reactor trains was divided into two separate reactor vessels where the
temperature
of the first 75-volume% containing 75 vol.% of the catalyst loading of that
reactor
could be independently controlled from the last 25-volume % of catalyst.
[0031] The operating conditions for the two trains were 1350 psig H2, liquid
hourly space velocities ("LHSV") of 1.4 vol./hr/vol., and 5500-6300 SCF/B of
hydrogen. The temperature schedule for both trains is described in Table 4
below.
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TABLE 3
50% 67% 100% 100%
Normal Normal Normal Heavy
FEED FCC MCO FCC MCO FCC MCO FCC MCO
API Gravity 18.1 15.0 9.5 7.0
Hydrogen, wt.% 10.65 10.04 8.77 8.61
Sulfur, wt.% 3.23 3.53 4.28 4.40
Nitrogen, ppm 959 1153 1485 1573
Aromatics-Mono, wt.% - - 12.0 8.8
Aromatics-Di, wt.% - - 43.9 41.7
Aromatics-Poly, wt.% - - 22.4 30.7
Distillation, D2887 GCD
498 493 485 493
50 627 625 618 642
90 703 705 706 749
95 726 721 724 777
TABLE 4
Days on Oil Feedstock 75%/25% Temperatures, F
4-6 50% FCC MCO 585/650
7-15 67% FCC MCO 585/650
16-30 100% FCC MCO 585-610/650-675
31-50 100% Heavy FCC MCO 610-635/675-700
[0032] The relative HDN volume activity of the stacked bed Catalyst C/Catalyst
A compared to Catalyst A is shown in the figure below. Note that for the 50%,
67% and 100% FCC MCO feeds the stacked bed system with only 25-volume % of
Catalyst A shows a stable activity advantage of 275%.
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[0033] As shown in the Figure, when the 100% Heavy FCC MCO was used as
the feed note the activity advantage for the stacked bed catalyst system
containing
begins to decrease from 275% to 225% and then was subsequently reduced over 20
days to slightly less than 150%.
EXAMPLE 3
[0034] In this Example, a stacked bed catalyst system containing 75 vol.% of
Catalyst B and 25 vol.% Nebula, both as described above, was used to
hydrotreat a
light cycle cat oil feed ("Feed A") and a heavier medium cycle cat oil feed
("Feed
B") as described in Table 5 below. Example 2 was conducted in the same two
reactor train pilot plant unit as described in Example 2 above. The operating
conditions for the two trains were 1200 psig H2, liquid hourly space
velocities of 2
vol./hr/vol., and 5000 SCF/B of hydrogen.
[0035] The reactor effluents were stripped with nitrogen in an oven at 100 C
to
remove substantially all of the gaseous reaction products. The nitrogen
content of
the liquid reactor effluent was then analyzed by ASTM 4629. The temperature
schedules for both trains along with the results of this example are described
in
Table 5 below.
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TABLE 5
FEED Feed A Feed B
API Gravity 0.973 0.9
Sulfur, wt.% 2.6 2.50
Nitrogen, ppm 713 742
Distillation, D2887 GCD
427 448
50 551 590
95 707 755
EP 764 823
Catalyst B Temperature 570 617
Nebula Temperature 645 692
Stripped Reactor Effluent
Nitrogen Content 2 7
Nitrogen Removal Relative
Volume Activity 1.75 1.75
[0036] As can be seen in Table 5, when a conventional catalyst having an
average pore diameter of 14 nm was used in the first 75 vol.% of the reactor,
the
Nitrogen Removal Relative Volume Activity ("RVA") for the catalyst system
remained constant when the heavier feed was used. In comparing the results of
Example 3 to those obtained in Example 2, one can see that when a catalyst
having
a pore volume of 7.5 nm preceded the bulk metal catalyst, the RVA of the
catalyst
system decreased. However, in Example 3, the heavier feed did not negatively
impact the RVA of the catalyst system.
